The invention relates to a method of computing surface acoustic wave ray paths on complex curved surfaces for use in laser applications such as ultrasound non-destructive evaluation (NDE). Laser ultrasonic imaging is used to generate high resolution images of an object and may be used to inspect a surface for defects. U.S. Pat. Nos. 5,760,904 and 5,801,312, assigned to the assignee of the present invention and incorporated herein by reference, disclose systems for imaging an object using laser ultrasound. Both of these patents disclose use of synthetic aperture focusing techniques (SAFT) to laser ultrasound generated surface waves for rapid wide-area imaging of surface and near surface defects from limited scan areas including single lines. The basic SAFT algorithm relies on what is referred to as the delay and sum method. In essence, it uses the ultrasound propagation delays between the source and image points over the inspected surface or volume.
The success of the SAFT is tied to knowing the surface acoustic wave (SAW) ray paths and wave fronts on the surfaces. On simple, Euclidean surfaces (e.g. flat surfaces) such paths can be easily defined by assuming a point source of sound in the far field and observing that the rays essentially trace out meridians or radii from the point source. For more complex surfaces, there is a need in the art for a method of tracing SAW ray paths and wave fronts on the surface to allow for laser ultrasound inspection of such complex surfaces.